Method and apparatus for coating resin

ABSTRACT

Method and apparatus for coating a surface of a work with a thin resin or plastic film suitable for use in imprinting a pattern by impressing a master pattern on a transfer surface of a mold on the coated resin film. A curable resin liquid is coated on a work by the use of an inkjet feed means having a plural number of inkjet nozzle holes in a row or rows on a nozzle assembly, in association with actuators to propel droplets of resin liquid from the respective inkjet nozzle holes in controlled timings while moving the inkjet feed means and the work relative to each other.

BACKGROUND OF THE INVENTION

1. Field of the Art

This invention relates to method and apparatus for coating a resin, andmore particularly to method and apparatus for coating a surface of asubstrate plate with a thin film of a curable resin or plastic suitablefor use in imprinting a pattern of infinitesimally minute dents andprojections.

2. Prior Art

In the so-called nano-imprinting, a rectilinear or circular pattern ofinfinitesimally minute dents and projections is transferred to a surfaceof a substrate plate of an arbitrary shape by a hot embossing, moldingor stamping process. In any case, a curable resin film is coated on asurface of a substrate plate in a preparatory stage. In the case of astamping process, a photo-setting synthetic resin is coated on asubstrate plate, followed by impression of a mold against the coatedresin film to transfer a pattern of minute dents and projections to thecoated plastic film from a transfer surface of the mold. While the moldis in an impressed state, the resin film is irradiated with light raysfor setting the resin. The substrate plate which comes out uponseparation from the mold has a pattern of minute dents and projectionstransferred on its surface.

With a substrate plate of a circular or annular shape, it has been thegeneral practice to coat the substrate plate with a resist film by theuse of a high speed spin machine as described in Japanese Laid-OpenPatent Application H6-333807, for example. Namely, in this case, a workin the form of a circular glass plate is put on a turn table, and, whilethe turn table is rotated at high speed, a resist liquid is dripped on awork surface from a resist liquid feed nozzle which is moved radiallyfrom the center to the outer periphery of the turn table. Since the workis rotated along with the turn table, the resist liquid is fed onto thework surface in a spiral shape and urged to flow in radially outwarddirections under the influence of centrifugal force to form a resistfilm over the entire surface of the work.

As described above, a resist liquid is applied by high speed spincoating in Japanese Laid-Open Patent Application H6-333807. In the caseof the high speed spin coating, a resist liquid is spread with the aidof centrifugal force. In that case, however, there is a difference incircumferential speed between inner and outer peripheral areas, so thatthe resist liquid is subjected to greater centrifugal force in outerperipheral portions than in inner peripheral portions, and as a result acoated resist film has different thicknesses in inner and outerperipheral portions of the substrate plate. Besides, in the case of thehigh speed spin coating as in Japanese Laid-Open Patent ApplicationH6-333807 mentioned above, there is a limit to reduction of filmthickness. That is to say, the method of Japanese Laid-Open PatentApplication H6-333807 can be suitably applied to a process for coating aresist film on a master of an optical disc, but cannot be applied to aprocess for coating an extremely thin resin film uniformly on a worksurface.

For example, to cope with the trends toward larger storage capacitiesand higher densities of semiconductor integrated circuits, magneticdiscs and optical discs, there have been developed and put in usenano-structure devices having a pattern of infinitesimally minute dentsand projections on a surface of a substrate plate. As described inJapanese Laid-Open Patent Application H6-333807 mentioned above, the hotembossing technology which is generally applied in the production of anoptical disc master has a limit in the size of minute dents andprojections to be formed on a substrate plate. Beside the hot embossing,neither the molding process nor the stamping process cannot be appliedto nano-imprinting in case of a pattern involving dents and projectionssmaller than several tens nanometers. This is because, in the case ofnano-imprinting, it is required to coat an extremely thin resin filmuniformly on a surface of a substrate plate and with extremely highaccuracy. At least from the standpoint of mass production, the high spedspin coating is unsuitable for application to a process formanufacturing resin-coated substrate plates which are strictlycontrolled in thickness of resin film.

SUMMARY OF THE INVENTION

In view of the above-discussed problem, it is an object of the presentinvention to make it possible to coat a surface of a substrate plateefficiently uniformly with an extremely thin resin film, which isparticularly suitable for use in imprinting a nano-pattern by impressinga master pattern on a transfer surface of a mold against the resin film.

In accordance with the present invention, in order to achieve theabove-stated objective, there is provided a resin coating apparatus forcoating a surface of a substrate plate with a thin resin film suitablefor use in imprinting a pattern by impressing thereon a master patternon a transfer surface of a mold, characterized in that said apparatuscomprises: an inkjet feed means having a plural number of inkjet nozzleholes in an array on a nozzle assembly to feed droplets of a resinliquid onto a surface of the substrate plate, each one of said inkjetnozzle holes being associated with an actuator to propel a droplet ofsaid resin liquid intermittently in a controlled timing; and a linear orrotational drive means adapted to move said inkjet feed means and thesubstrate plate relatively at least in a direction perpendicular to thearray of the inkjet nozzle holes or in a rotational direction.

In this instance, the substrate plate is not limited to a particularshape. For example, it may be in a circular shape like semiconductorwafers and optical parts, may be in an annular shape like magnetic oroptical discs, or may be in square or other arbitrary shapes. The resinto be coated on a substrate plate is a curable resin which can be set byirradiation of light rays including ultraviolet rays or by heating orcooling.

The inkjet feed means has a plural number of inkjet nozzle holes arrayedin a predetermined direction on a nozzle assembly, in association withactuators like piezoelectric elements thereby propelling droplets of aresin liquid out of the respective inkjet nozzle holes intermittently incontrolled timings for deposition on the substrate plate surface. Atleast one of the inkjet feed means or the substrate plate is movedrelative to the other one by means of a linear or rotational drivemeans. In case of a linear drive, it is adapted to move either theinkjet feed means or a substrate plate in a direction perpendicular tothe array of the inkjet nozzle holes on the nozzle assembly. In case ofa rotational drive, the inkjet nozzle holes are arrayed in a row or rowsin a radial direction of a substrate plate. Pico-order droplets arepropelled from the respective inkjet nozzle holes. The thickness of theresin film can be controlled by way of the size of droplets of resinliquid and the number of droplets to be fed per unit area of a substrateplate.

In a case where a resin liquid is fed onto a surface of an annularsubstrate plate, the inkjet resin feed means has inkjet nozzle holesarrayed in a row or rows on a nozzle assembly, which is long enough forcovering at least the diameter or radius of the substrate plate. In thiscase, either the inkjet nozzle assembly or the substrate plate is put inrotation by the drive means. In a case where the substrate plate is putin rotation, the rotational speed should be controlled to a low level atwhich droplets of resin liquid can be deposited free of influences ofcentrifugal force. The inkjet nozzle holes which are arrayed in theradial direction of the substrate plate are so controlled that dropletsof resin liquid are fed at longer time intervals in the inner peripheralside of the substrate plate than in the outer peripheral side. Namely,in consideration of differences in circumferential length, the timing ofdrop feed is shortened from the inner to outer periphery of thesubstrate plate. Thus, droplets of resin liquid are deposited and coateduniformly on the entire surface of a substrate plate from the inner toouter periphery.

Further, according to the present invention, there is also provided amethod for coating a surface of a work with a thin resin film suitablefor use in imprinting a pattern by impressing thereon a master patternon a transfer surface of a mold, characterized in that the methodcomprises the steps of: providing an inkjet feed means having a pluralnumber of inkjet nozzle holes in a nozzle assembly; positioning thenozzle assembly face to face with a coating surface of the work; andpropelling droplets of a resin liquid toward the work from therespective inkjet nozzle holes while moving the work relative to theinkjet feed means or vice versa.

The above and other objects, features and advantages of the presentinvention will become apparent from the following particular descriptionof the invention, taken in conjunction with the accompanying drawingswhich show by way of example preferred embodiments of the invention.Needless to say, the present invention should not be construed as beinglimited to particular forms shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic illustration explanatory of steps of anano-imprinting process;

FIG. 2 is a schematic view of a pattern of nano-order dents andprojections imprinted on a surface of a substrate plate;

FIG. 3 is a schematic front view of a resin coating apparatus;

FIG. 4 is a schematic plan view of the resin coating apparatus shown inFIG. 3; and

FIG. 5 is a schematic sectional view showing construction of an inkjetnozzle on an inkjet means.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereafter, with reference to the accompanying drawings, the presentinvention is described more particularly by way of its preferredembodiments. Reference is first had to FIG. 1 which schematically showssteps of a nano-imprinting process for imprinting a photo-setting resinor plastic. As shown at (a) of that figure, an ultraviolet-setting resinR is coated on a surface of a glass substrate plate S of the sort whichis generally used for a data recording medium. In this instance, theresin R is in the form of a liquid, and, as shown in FIG. 1(b), a masterpattern of dents and projections on a transfer surface of a mold M istransferred to the resin R by impressing the mold M under pressure.While the mold M is in a pressed state, the resin R is cured byirradiation of ultraviolet rays UV. Thereafter, upon separating the moldM as shown in FIG. 1(c), there comes out a substrate plate S which hasminute projections P transferred and imprinted on its surface. In thisstate, however, a base layer B still remains on the substrate surface.Therefore, the substrate plate S is immersed in a predetermined solutionto remove the base layer B as shown in FIG. 1(d).

In a nano-imprinting process as described above, it is an imperativerequisite for the resin R to be coated in uniform thickness. If a coatedresin film has variations in thickness, it becomes difficult to transferminute dents and projections of nano order accurately by impression of amold M. Besides, in consideration of the necessity of exfoliation of abase layer B, a resin M should not be coated in a redundantly largethickness. Through the steps shown in FIG. 1, a multitude of minuteprojections in a concentric pattern are formed on the surface of thesubstrate plate S as shown in FIG. 2. In this instance, for use as adata recording medium, the respective projections P should beinfinitesimally minute in dimensions and yet should be uniform in shape.For instance, in order to imprint projections P which are 100 nm inheight and 30 nm in diameter and spaced from each other by an intervalof 100 nm, along with a base layer of a thickness of 5 nm±2 nm, theresin R should be coated on a substrate plate S in a thickness ofapproximately 100 nm to 120 nm.

In order to coat a resin R in the form of such an extremely thin film, aresin liquid is fed onto the surface of a substrate plate S bydrop-feeding, using an inkjet resin feed means as shown in FIGS. 3 and4. As shown in these figures, a substrate plate S is rotatably set on aspindle 1, face to face with an inkjet resin feed means 10. The inkjetresin feed means 10 is provided with a bar-like manifold nozzle assembly12 at the lower end of a vertical pendant shaft 11. A multitude ofnozzle holes are bored in the nozzle assembly 12 at very small intervalsin the longitudinal direction of the nozzle assembly 12. The pendantshaft 11 is located vertically in alignment with the center of rotationof the spindle 1, and arranged to support the bar-like nozzle assembly12 in a horizontal position in such a way as to fully cover the wholediameter of the substrate plate S on the spindle 1. In the case of theparticular inkjet resin feed means 10 shown in the drawing, the nozzleholes 13 are bored in two rows in the longitudinal direction of thenozzle assembly 12. The pendant shaft 11 of the inkjet means 10 is atleast movable up and down in the vertical direction. If necessary,arrangements may be made to move the inkjet resin feed means 10 in adirection perpendicular to the vertical pendant shaft 11.

As shown in FIG. 5, the respective nozzle holes 13 on the nozzleassembly 12 are communicated with a resin liquid supply passage 14,which in turn is connected to a resin liquid reservoir tank (not shown)through the pendant shaft 11. On the side away from the side in whichthe inkjet nozzle holes 13 are opened, the nozzle assembly 12 isprovided with a flexible membrane 15 in association with piezoelectricelements 16 (indicated in FIGS. 3 and 4 as piezoelectric assembly units16U mounted in association with the inkjet nozzle holes 13 on theopposite sides of the pendant shaft 11) which function as actuators forcontrolling the resin liquid drop-feed rate from the respective ink jetnozzles 13. Thus, each time a piezoelectric element 16 of an inkjetnozzle hole 13 is driven, the flexible membrane 15 are pushed to apply apressure to a resin liquid in the resin liquid supply passage 14,propelling a droplet of resin liquid out of that inkjet nozzle hole 13.In this manner, the drop feed of resin liquid from the respective nozzleholes 13 can be controlled separately and independently of each other.For this purpose, the inkjet resin feed means 10 is provided with acontrol circuit 17 thereby to drive the respective piezoelectricelements 16 in controlled timings.

In this instance, each time, a droplet of resin liquid of several to tenand several picoliters is propelled out of each inkjet nozzle hole 13toward the surface of the substrate plate S. In order to preventdroplets of resin liquid from splashing off the surface of the substrateplate S, the resin liquid is supplied from the nozzle assembly 12 whichis located in small gap relation with the substrate plate S, morespecifically, at a space of 1 to 3 mm from the surface of the substrateplate S, while controlling the voltage to be applied to the respectivepiezoelectric elements 16.

By the use of the inkjet resin feed means 10 as described above, anextremely thin resin film is coated uniformly on the entire surface of asubstrate plate S. More specifically, a substrate plate S is set on thespindle 1, and the inkjet resin feed means 10 is positioned face to facewith the substrate plate S. While the substrate plate S is put inrotation by the spindle 1, droplets of resin liquid are propelled out ofthe respective nozzle holes 13 on the nozzle assembly 12 and depositedon the surface of the substrate plate S. At this time, a droplet ofresin liquid is fed at longer time intervals from inkjet nozzle holes 13facing inner peripheral portions of the substrate plate S, that is tosay, droplets of resin liquid are fed from the inkjet nozzle holes 13 atshorter time intervals in outer peripheral portions of the substrateplate S where a drop feed circumferential length becomes greater. Thatis to say, a droplet of resin liquid is propelled at the shortest timeintervals from inkjet nozzle holes 13 radially in the outermostposition. The inkjet nozzle holes 13 are driven separately andindependently by piezoelectric elements 16 which are provided in therespective inkjet nozzle hole 13. Drop feed timings of the respectiveinkjet nozzle holes 13 are controlled and varied by the afore-mentionedcontrol circuit 17, shortening the drop feed time intervals from theinner to outer periphery of the substrate plate S as mentioned above.

Thus, as described above, a thin film of a resin R, approximately 100 nmin thickness, can be coated uniformly over the entire surface of asubstrate plate S by feeding droplets of resin liquid by the use of theinkjet feed means 10. Accurate nano-imprinting is feasible simply byimpressing a master pattern on a transfer surface of a mold against thecoated resin R.

1. A resin coating apparatus for coating a surface of a substrate platewith a thin resin film suitable for use in imprinting a pattern byimpressing thereon a master pattern on a transfer surface of a mold,characterized in that said apparatus comprises: an inkjet feed meanshaving a plural number of inkjet nozzle holes in an array on a nozzleassembly to feed droplets of a resin liquid onto a surface of saidsubstrate plate, each one of said inkjet nozzle holes having an actuatorto propel a droplet of said resin liquid intermittently in a controlledtiming; and a linear or rotational drive means adapted to move saidinkjet feed means and said substrate plate relatively at least in adirection perpendicular to said array of said inkjet nozzle holes or ina rotational direction.
 2. A resin coating apparatus as set forth inclaim 1, wherein said substrate plate is in the form of an annular disc,said inkjet nozzle holes on said nozzle assembly are arrayed in a row orin rows extending over a length sufficient to fully cover whole diameterof said substrate plate, and said drive means is adapted to put eithersaid substrate plate or said nozzle assembly in rotation; said inkjetfeed means further comprising a control circuit adapted to control dropfeed timings from said inkjet nozzle holes in such a way that dropletsof said resin liquid are fed onto said substrate plate at shorter timeintervals in outer peripheral side than in inner peripheral side of saidsubstrate plate.
 3. A resin coating apparatus as set forth in claim 2,wherein said nozzle assembly is located at a space of 1 to 2 mm from acoating surface of said substrate plate.
 4. A method for coating asurface of a work with a thin resin film suitable for use in imprintinga pattern by impressing thereon a master pattern on a transfer surfaceof a mold, characterized in that said method comprises the steps of:providing an inkjet feed means having a plural number of inkjet nozzleholes in a nozzle assembly; positioning said nozzle assembly face toface with a coating surface of said work; and propelling droplets of aresin liquid toward said work from the respective inkjet nozzle holeswhile moving said work relative to said inkjet feed means or vice versa.